Pure Substance and Mixture Viscosities Based on Entropy Scaling and an Analytic Equation of State

Abstract

This study proposes a simple model for viscosities, based on entropy scaling, for real substances and mixtures. The residual entropy is calculated with the perturbed chain polar statistical associating fluid theory (PCP-SAFT). The model requires two or three pure component parameters, noting, however, that an entirely predictive group contribution approach as proposed in our previous work [Loetgering-Lin O.; Gross J. Ind. Eng. Chem. Res. 2015, 54, 7942−7952] gives also very good results. Overall, 140 real substances are considered with relative mean deviations from experimental data of about 5% (without excluding "outliers"). We performed molecular simulations for mixtures of simple model fluid in order to determine a suitable mixture model. A completely predictive approach for viscosities of real mixtures is thereby obtained. The model is evaluated for 566 mixtures with about 34,500 experimental data points of various complexity (i.e., nearly ideal systems as well as highly asymmetric mixtures). Mixtures of nonpolar substances and mixtures with at least one polar, but nonhydrogen-bonding component, are predicted very accurately with relative mean deviations of on average 6.2% (173 mixtures considered) and 5.3% (126 mixtures considered), respectively. Limitations of the model are found for mixtures with hydrogen-bonding (associating) components such as amines and alcohols, where deviations are systematically higher. Lastly, we present results of mixture viscosities using the purely predictive group contribution framework and find similar results for the predictive approach.

Excess-entropy scaling in supercooled binary mixtures

“…This has also been found for other ionic melts in the supercooled region 62 . On the other hand, Lötgering-Lin et al 36 found collapse with composition of binary Lennard–Jones (LJ) mixtures in the high-temperature regime over a limited range in viscosity (factor of two). A related result has also been found for the computer-simulated metallic alloy AlNi in the high-temperature limit 32 .…”

Dynamic Viscosity of Binary Fluid Mixtures: A Review Focusing on Asymmetric Mixtures

“…A very detailed summary of the theoretical background and mathematical relations of entropy scaling with respect to viscosity predictions was recently published by Dyre [41] and is, therefore, not repeated here. For the calculation of viscosities of real fluids, this approach was primarily used in connection with semi-empirical equations such as the PCP-SAFT [42][43][44] or the CPA [45] equation of state. After introducing a modified approach with a dimensionless residual entropy per unit volume as the independent scaling variable and a suitable choice of a reference fluid for refrigerants [46], the approach was first applied to model fluids in conjunction with accurate Helmholtz-energy equations of state [47].…”

Low-GWP alternative refrigerant blends for HFC-134a :

“…87 Additional studies have demonstrated that the general framework of modified residual entropy scaling allows for an excellent collapse of the experimental transport data for other systems, including the viscosity of propane 88 , normal alkanes 89 , and refrigerants. 90 Other researchers [91][92][93][94] have applied an older variant of entropy scaling to refrigerant mixtures, but their overall approach of reducing by the dilute-gas viscosity does not follow the correct theoretical constraints in the liquid phase, which is particularly problematic for small molecules like methane and argon.…”